This invention relates to a method of adjusting color purity for color cathode ray tubes.
Various adjustments must be performed on a color cathode ray tube of a television receiver to achieve faithful color reproduction on the cathode ray tube screen of a transmitted picture. These adjustments may be performed after assembling components, such as the deflection yoke, purity and convergence devices on the cathode ray tube neck, but before installation of the assembled tube in the receiver chassis; alternatively, they may be performed after installation of the assembled tube into the chassis housing.
The types of adjustments required for typical in-line cathode ray tubes include: (1) center purity; (2) yoke pullback or positioning of deflection yoke at the proper location along the cathode ray tube central axis to achieve overall color purity; (3) static or center convergence; and (4) overall convergence. These four adjustments are performed in a prescribed order which may vary with different tube and yoke combinations. Furthermore, they may be performed at differing station points during the assembly and/or installation process.
Conventional techniques for adjusting color purity usually involve adjusting center purity with the yoke pulled back away from the cathode ray tube screen as far as practical. Center purity is then adjusted with conventional apparatus, such as rotatable two-pole magnetic purity rings located about the cathode ray tube neck. Overall purity is then obtained by repositioning the yoke along the central axis until the deflection planes of the yoke and the cathode ray tube coincide.
For some cathode ray tube/deflection yoke combinations, there may be insufficient separation between one end of the yoke housing and the other apparatus located on the cathode ray tube neck to provide sufficient yoke pullback to permit center purity adjustment. It is desirable, therefore, to use a purity adjustment method that does not require yoke pullback. This method must be sufficiently flexible to be readily adaptable for use with various cathode ray tubes, yokes, and other components combinations, and readily adaptable to various adjustment sequences, and to be used at various station points during the cathode ray tube assembly and/or installation.